Tubesheets are a component of many types of fluid filtration modules including those used in both gas and liquid separations. A tubesheet comprises a plurality of aligned semi-permeable hollow fiber membranes (i.e. “bundle”) including end segments that are embedded (i.e. “potted”) within a block of resinous potting material. The ends of the fibers may terminate within the potting material or extend therethrough to expose open lumens of the fibers. When fabricated into a module, the tubesheet provides a seal about the periphery of individual fibers and prevents fluid passage except via the lumens of the fibers. Depending upon the configuration of the module, the tubesheet may form a seal with the inner walls of a housing (e.g. U.S. Pat. No. 5,192,478) or a submergible header (e.g. US 2009/0026140; US 2005/0126982; U.S. Pat. No. 6,214,226; U.S. Pat. No. 6,294,039 and U.S. Pat. No. 7,160,454). Examples of tubesheets, methods for making tubesheets and modules incorporating tubesheets are provided in: U.S. Pat. No. 3,722,695; U.S. Pat. No. 4,138,460; U.S. Pat. No. 5,192,478; U.S. Pat. No. 6,290,756; U.S. Pat. No. 7,662,333 and JP 2009-125642. Specific potting techniques include centrifugal potting (e.g. U.S. Pat. No. 6,974,554) and the use of a mold structure with perforated plates (e.g. US 2007/0158257; U.S. Pat. No. 5,840,230 and JP 07-32867).
Fibers of tubesheets are susceptible to damage at or near the interface of the potting material. This is at least partially due to a lack of flexibility of the fiber near the interface with the potting material. Various techniques for ameliorating this effect are described in the literature including the use of multilayer potting layers (e.g. U.S. Pat. No. 3,708,071; U.S. Pat. No. 6,290,756; U.S. Pat. No. 6,974,554 and US 2007/0158257), adhesive layers (e.g. U.S. Pat. No. 6,592,759) and the use of fiber coatings near the potting interface (e.g. U.S. Pat. No. 5,192,478; U.S. Pat. No. 7,344,645; U.S. Pat. No. 7,704,393 and JP 2005-52716). These techniques address the outer periphery of the fiber and often require the use of multiple compositions and or process steps, e.g. potting with an inner layer of rigid epoxy potting material and an outer layer of a more flexible epoxy, silicone or polyurethane material.